The Lie

In his book the Republic, Plato states through Socrates that in his city the youth should not be told of many things. Stories that tell of disobeydience or treachery and music that might corrupt them would be banned. The consequences of this, are said to be the enlightenment of the youth and the ending of many hostilities which might arise. Two questions come to mind. Would such a Lie be possible to maintain? Would it indeed be a good and thing and end evil?